1. Field of Invention
The present invention relates to electrochromic devices, and more particularly to electrochromic devices having dual-layer ion conductors and methods for making such ion conductors.
2. Description of the Prior Art
Electrochromic materials are materials that change their optical properties as the result of an applied electrical potential. Such materials can be used to produce electrochromic devices that can vary the transmission or reflectance of electromagnetic radiation via application of an electrical potential. FIGS. 1 and 2 depict a typical prior art electrochromic device 100. Electrochromic device 100 includes an electrochromic (EC) layer 101, an ion conductor (IC) layer 102 and a counter-electrode (CE) layer 103, which may also be electrochromic. Layers 101-103 are positioned between two transparent conducting oxide (TCO) layers 104 and 105.
Typically, EC layer 101 is a cathodic electrochromic material, such as WO3, and CE layer 103 is an anodic electrochromic material, such as nickel oxide NiOx. With ion incorporations, anodic electrochromic materials become bleached (high optical transmission state), whereas cathodic electrochromic materials become colored (low optical transmission state). The ions that move between EC layer 101 and CE layer 103 can be hydrogen ions (H+), lithium ions (Li+), or alkali and alkaline earth ions. When an electrical current is applied through TCO layers 104 and 105 across the EC/IC/CE layers (layers 101/102/103), ions are shuttled between EC layer 101 and CE layer 103 through IC layer 102, leading to switching between bleached and colored states. When in the bleached state, light and heat that is incident on an electrochromic device passes through the device. When in the colored state, only a portion of the light and heat incident on the electrochromic device passes through the device. FIG. 1 depicts an electric potential (e.g. battery 10) being applied between TCO layer 104 and TCO layer 105, and electrochromic device 100 in a bleached state. FIG. 2 depicts a reverse electric potential e.g. battery 210) being applied between TCO layer 015 and TCO layer 104, and electrochromic device 100 in a colored state.
In FIGS. 1 and 2, IC layer 102 serves to electronically insulate EC layer 101 from CE layer 103, while allowing ions to go through. Pinholes in IC layer 102 result in electronic shorts, which can grow with time and usage, thereby resulting in poor reliability, device yield, and color memory. An inorganic solid state thin-film IC layer 102, such as Ta2O5, is often used in electrochromic 17 switchable-window applications because of its durability with respect to UV and its sturdiness. An inorganic IC layer is often deposited via physical vapor deposition (PVD), such as sputtering or evaporation, or chemical vapor deposition (CVD) techniques, which lead to many pinholes, especially in large-area window applications.
Dual-layer IC layers have been used to address layer delamination and electron flow problems. U.S. Pat. No. 5,777,779 teachers a dual-layer ion conductor layer intended to increase the bond between layers in an electrochromic device. The dual-layer IC layer is formed by processing a first portion of the IC in an atmosphere with water vapor and a second portion of the IC in an atmosphere containing oxygen. U.S. Patent Application Pub. No. 2007/0097481 describes an IC having at least three layers, including two ion transport layers separated by a buffer layer. The three layer IC is used to block electron flow in both directions while permitting ionic conduction, allowing an electrochromic device to have greater dynamic range and stability.